The state-of-the-art method of manufacturing toner includes a number of processes such as the mixing of suitable components, extrusion, cooling, and downstream comminution. The comminuted material is then routed to a downstream classifying process with the aim of removing the undesirable particle fractions and of producing an end product of the desired particle size distribution. The particle size distribution (PSD) is usually measured with a Coulter Counter Multisizer made by Coulter Electronics, Inc., USA. The objective of the classifying process is generally the separation of extremely fine particles in the range under 5 .mu.m, but is sometimes also achievement of an upper particle limit or of both objectives together.
For this purpose, conventional processes use classifiers as are known from German patent DE 39 15 641 A1. With such classifiers, in which there is no controlled product feed, the classified product can backmix with the feed product. This leads to the product becoming contaminated by undesirable fines, which adversely affects the success of the classifying process. Furthermore, the dispersion of the feed material directly upstream of the classifying chamber in these classifiers is inadequate, meaning that agglomerates can form and thus transport particles which are actually too fine into the coarse material. This type of contamination, where fine particles contaminate the end product, can lead to a loss of quality when using the toner for printed images.